The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein, or any publication specifically or implicitly referenced herein, is prior art, or even particularly relevant, to the presently claimed invention.
Cardiovascular Diseases and Disorders
Ischemic heart disease is the leading cause of death in the U.S. Each year approximately 1.5 million people suffer heart attacks (myocardial infarctions), of which ⅓ (i.e. about 500,000) are fatal. In addition, about 6.75 million Americans suffer from angina pectoris, the most common manifestation of cardiac ischemia. Angina pectoris is a painful feeling of pressure in the chest that results from ischemic heart disease. In total, there are 13.5 million patients living with ischemic heart disease in the U.S. Americans in the high-risk categories for this disease include persons having one or more indicators/risk factors therefor, including but not limited to hypertension, high levels of serum cholesterol and a family history of heart disease. Many people have at least one of these indicator/risk factors; for example, there are 50 million Americans diagnosed with hypertension alone.
“Ischemia” is a condition associated with an inadequate flow of oxygenated blood to a part of the body, typically caused by the constriction or blockage of the blood vessels supplying it. Ischemia occurs any time that blood flow to a tissue is reduced below a critical level. This reduction in blood flow can result from: (i) the blockage of a vessel by an embolus (blood clot); (ii) the blockage of a vessel due to atherosclerosis; (iii) the breakage of a blood vessel (a bleeding stroke); (iv) the blockage of a blood vessel due to acute vasoconstriction; (v) a myocardial infarction (when the heart stops, the flow of blood to organs is reduced and ischemia results); (vi) trauma; (vii) surgery, during which blood flow to a tissue or organ needs to be reduced or stopped to achieve the aims of surgery (e.g., angioplasty, heart and lung/heart transplants); (viii) exposure to certain agents, e.g., dobutamine or adenosine (Lagerqvist et al., Br. Heart J. 68:282–285, 1992) or (ix) anti-neoplastic and other chemotherapeutic agents, such as doxorubicin, that are cardiotoxic.
Even if the flow rate (volume/time) of blood is adequate, ischemia may nonetheless occur due to hypoxia. “Hypoxia” refers to conditions in which the oxygen content of blood is insufficient to satisfy normal cellular oxygen requirements. Hypoxic blood is, by definition, distinct from normoxic blood, i.e., blood in which the oxygen content is sufficient to satisfy normal cellular oxygen requirements. Such conditions include but are not limited to forms of heart failure that adversely affect cardiac pumping such as hypertension, arrhythmias, septic shock, trauma, cardiomyopathies and congestive heart disease.
Myocardial ischemic disorders occur when cardiac blood flow is restricted (ischemia) and/or when oxygen supply to the heart muscle is compromised (hypoxia) such that the heart's demand for oxygen is not met by the supply. Coronary artery disease (CAD) arising from arteriosclerosis, particularly atherosclerosis, is the most common cause of ischemia, and has symptoms such as stable or unstable angina pectoris. CAD can lead to acute myocardial infarctions (AMI) and sudden cardiac death. The spectrum of ischemic conditions which result in heart failure is referred to as Acute Coronary Syndrome (ACS). Reperfusion injury is often a consequence of ischemia, in particular when anti-coagulants, thrombolytic agents, or anti-anginal medications are used or when the cardiac vasculature is surgically opened by angioplasty or by coronary artery grafting.
Cardiotoxic agents are those materials which would cause a loss of cardiac function, including negative inotropy, arthyTHmias, heart failure, and cell death (both apoptotic and necrotic).
Presently, treatments for acute myocardial infarction and other cardiac diseases include but are not limited to mechanical devices and associated procedures therewith (e.g., coronary angioplasty; Grines et al., N. Engl. J. Med. 3298:673–679, 1993); thrombolytic agents such as streptokinase, tPA, and derivatives thereof. Adjuvants to these therapies include beta-blockers, aspirin and heparin, and glycoprotein (GP) IIb/IIIa inhibitors (Antman et al., Circ. 99:2720–2732, 1999). GP IIb/IIIa inhibitors decrease platelet aggregation and thrombus formation (for a review, see Topol, Lancet 353:227–231, 1999). Examples include but are not limited to monoclonal antibodies (e.g., abciximab), cyclic peptides (e.g., eptifibatide), and nonpeptide peptidomimetics (e.g., tirofibian, lamifiban, xemilofiban, sibrafiban, and lefradafibian).
Preventive treatments include but are not limited to those that reduce a patient's cholesterol levels by, e.g., diet management and pharmacological intervention. Statins are one type of agent that have been used to reduce cholesterol levels. Statins are believed to act by inhibiting the activity of HMG-CoA reductase, which in turn increases the hepatic production of cholesterol receptors (Nickenig et al., Circ. 100:2131–2134, 1999). The hepatic cholesterol receptors bind cholesterol and remove it from blood. Such agents include but are not limited to lovastatin, simvastatin, pravastatin, fluvastatin (Lennernas, Clin. Pharmackinet. 32:403–425, 1997). These and other statins slows the progression of coronary artery disease, and may induce regression of atherosclerotic lesions in patients. It is not known, however, whether other reductases are inhibited by such agents, and what side effects might occur as a result.
Cerebrovascular Diseases and Disorders
Patients experiencing cerebral ischemia often suffer from disabilities ranging from transient neurological deficit to irreversible damage (stroke) or death. Cerebral ischemia, i.e., reduction or cessation of blood flow to the central nervous system, can be characterized as either global or focal.
Focal cerebral ischemia refers to cessation or reduction of blood flow within the cerebral vasculature resulting from a partial or complete occlusion in the intracranial or extracranial cerebral arteries. Such occlusion typically results in stroke, a syndrome characterized by the acute onset of a neurological deficit that persists for at least 24 hours, reflecting focal involvement of the central nervous system and is the result of a disturbance of the cerebral circulation. Other causes of focal cerebral ischemia include vasospasm due to subarachnoid hemorrhage or iatrogenic intervention.
Global cerebral ischemia refers to reduction of blood flow within the cerebral vasculature resulting from systemic circulatory failure. The failure of the circulatory system to maintain adequate cellular perfusion leads to a in reduction of oxygen and nutrients to tissues. Thus, global cerebral ischemia results from severe depression of cardiac performance. The most frequent cause is acute myocardial infarction with loss of substantial muscle mass. Pump failure can also result from acute myocarditis or from depression of myocardial contractility following cardiac arrest or prolonged cardiopulmonary bypass. Mechanical abnormalities, such as severe valvular stenosis, massive aortic or mitral regurgitation, acutely acquired ventricular septal defects, can also reduce cardiac output. Additional causes include cardiac arrhythmia, such as ventricular fibrillation, and any cardiac disease described herein. Further causes include interventional procedures, such as carotid angioplasty, stenting or endarterectomy, which might otherwise result in focal cerebral ischemia, and also cardiac procedures which may result in global cerebral ischemia, such as cardiac catheterization, electrophysiologic studies, and angioplasty.
Those skilled in the art are easily able to identify patients having a stroke or at risk of having a stroke, cerebral ischemia, head trauma, or epilepsy. For example, patients who are at risk of having a stroke include, but are not limited to, patients having hypertension or undergoing major surgery.
Traditionally, emergent management of acute ischemic stroke consists of mainly general supportive care, e.g. hydration, monitoring neurological status, blood pressure control, and/or anti-platelet or anti-coagulation therapy. Heparin has been administered to stroke patients with limited and inconsistent effectiveness. In some circumstances, the ischemia resolves itself over a period of time due to the fact that some thrombi get absorbed into the circulation, or fragment and travel distally over a period of a few days. In 1996, the Food and Drug Administration approved the use of tissue plasminogen activator (t-PA) or Activase®, for treating acute stroke. However, treatment with systemic t-PA is associated with increased risk of intracerebral hemorrhage and other hemorrhagic complications. Aside from the administration of thrombolytic agents and heparin, there are no therapeutic options currently on the market for patients suffering from occlusion focal cerebral ischemia. Vasospasm may be partially responsive to vasodilating agents. The newly developing field of neurovascular surgery, which involves placing minimally invasive devices within the carotid arteries to physically remove the offending lesion may provide a therapeutic option for these patients in the future, although this kind of manipulation may lead to vasospasm itself.
Documents
U.S. Pat. No. 6,210,976 B1 and published PCT patent application WO98/57179 (PCT/US98/10486), both entitled “Methods for Early Detection of Heart Disease”, hereby incorporated by reference, relate to the use of blood levels of certain sphingolipids for screening for early ischemic events before symptoms are presented in persons with high risk for heart disease, or in a triage setting for patients with acute coronary syndrome.
PCT Application PCT/US01/12706, published as WO 01/80903, entitled “Detection and Treatment of Atherosclerosis Based on Plasma Sphingomyelin Concentration”, relates to enzymatic methods to measure plasma and tissue sphingomyelin concentrations, and that human plasma sphingomyelin levels are positively correlated with atherosclerosis and coronary heart disease.
U.S. Pat. No. 5,929,039, entitled “Method for Treating Cardiac Dysfunction and Pharmaceutical Compositions Useful Therefor”, relates to disclose methods methods for the prophylaxis or treatment of cardiac arrhythmia using an agent capable of blocking or inhibiting the effect or release of inositol(1,4,5)trisphosphate in cardiac tissue. The agent may be an aminoglycoside, including gentamicin.
U.S. Pat. No. 5,677,288, entitled “Use of Aminoglycosides to Protect Against Excitotoxic Neuron Damage”, relates to the use of an aminoglycoside, which may be gentamicin, that suppresses the flow of calcium ions into neurons through N-type calcium channels. The method relates to reducing excitotoxic damage to neurons, which can occur as a result of stroke, cerebral ischemia/hypoxia, or other events or conditions.
Published U.S. Patent Application 20010041688, entitled “Methods and Compositions for the Regulation of Vasoconstriction”, relates to modulation of sphingosine kinase and sphingosine-1-phosphate phosphatase activity and EDG receptor signaling for the treatment of conditions relating to vasoconstriction and vasoconstriction, including migraine, stroke, subarachnoid hemorrhage and vasospasm.
Ancellin et al., “Extracelluar export of sphingosine kinase-1 enzyme: Sphingosine 1 phosphate generation and the induction of angiogenic vascular maturation”, JBC Papers in Press. Published on Dec. 10, 2001 as manuscript M102841200 relates to events related to angiogenosis that are mediated by a sphingosine kinase.